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Becht Engineering Blog

In this section of the site contributing authors submit interesting articles relating to the various services, industries and research & development efforts of Becht Engineering.

When Should the Rules for Severe Cyclic Conditions (Service) in ASME B31.3 Be Used?

process_piping_ASME_B31
This posting (November 2019) is an update to an October 2013 post which reflects changes to the ASME B31.3 Code relative to severe cyclic service that have occurred since the original post.There has been a fair amount of confusion as to when the rules for severe cyclic conditions in ASME B31.3 should be used, and the rules themselves can be somewhat confusing to apply. In the 2016 edition of ASME B31.3 the definition of when the rules for severe cyclic service are applicable were changed, which may reduce the confusion.  The definition as to when the rules of severe cyclic apply is in the 300.2, Definitions.  Prior to the 2016 edition, it stated that severe cyclic conditions are:Conditions applying to specific piping components or joints in which SE computed in accordance with para. 319.4.4 exceeds 0.8SA (as defined in para. 302.3.5); andThe equivalent number of cycles (N in para. 302.3.5) exceeds...
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Recent Comments
Guest — Rohit Patel

ASME B31.3

Thanks for showing the Rules for Severe Cyclic Conditions (Service) in ASME B31.3 Be Used.
Monday, 16 December 2019 05:48
Guest — Hafiz Ali Alvi

Impact on Wall thickness for C...

Dear Mr. Becht, I would like to ask what could be possible impact of cyclic service for the calculated pipe wall thickness under p... Read More
Saturday, 16 November 2019 23:59
Chuck Becht

Impact on Wall thickness for C...

Designation of a system as being in severe cyclic service does not impact the wall thickness calculations for pressure design. No... Read More
Sunday, 17 November 2019 07:40
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Resolution of Chronic Cooling Tower Fan Vibrations

Resolution of Chronic Cooling Tower Fan Vibrations
Traditional rotating equipment mounted at grade use the mass of a foundation and grout to reduce vibration and provide support and stiffness. However, cooling tower fans must be elevated many feet above a basin of water which sometimes puts them “out of sight and out of mind”. Cost and practicality prohibits concrete and grout, thus most cooling towers are constructed by bolted wood and / or fiberglass elements with a fabricated steel sub base supporting motor, gearbox, and blades. As a result, cooling tower foundations are much less stiff than traditional rotating equipment. This is usually not an issue because the low speed of the fan (usually 60 rpm to 140 rpm) does not usually produce large forces. Motors and gearboxes used are generally made to the same precision levels as other general purpose machinery regarding balance, runout and dimensional tolerances, so the imbalance and forcing functions are usually low.  As...
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“Speed Kills” – An Empirical Association of Antifriction Bearing Behavior When Things Go From Bad to Worse

“Speed Kills” – An Empirical Association of  Antifriction Bearing Behavior When Things Go From Bad to Worse
Machinery and reliability people have for a long time observed that when it comes to long life and high reliability, operating at higher speeds compares poorly to operation at lower speeds.One of the primary reasons for having high-speed devices is economics. With high speed you can have smaller equipment sizes with fewer stages. While capacity and pressures developed do improve, this often occurs at the cost of increased wear, vibration, noise and maintenance.There are some limits as to how fast and large we can practically go. At some point even the required lubrication systems become very complex. While smaller equipment can use antifriction/rolling element bearings, their application is typically limited by manufactures to a certain speed. When combined with the bearing size, this limit becomes known as a DN number limit, a product of the mean bearing diameter (ID+OD in mm divided by 2) and the RPM. This DN limit is...
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No Detail or Procedure is Trivial, or, Sophisticated Vibration Analysis is a VERY Cost Effective Diagnostic Tool

No Detail or Procedure is Trivial, or, Sophisticated Vibration Analysis is a VERY Cost Effective Diagnostic Tool
Today it is common practice in overhauls of large rotating equipment to spend many man hours in detailed planning, coordination, writing procedures, reviewing documentation, reviewing past photos, procuring and inspecting spare parts etc. We also review our past experience and put steps in place to mitigate past problems or errors.   Now that we have a detailed plan, have purchased and inspected all necessary spare parts and have mitigated all potential known problems we simply give the plan to the machinery contractor to execute, right? If you have been responsible for large machinery repairs long enough, you have definitely learned to say one thing: “I have not seen everything,” and never to say another “Oh that could never happen here.” No matter how thorough we think our plan is, going in, missing even the slightest detail in the field can result in a failed start up or worse. Experienced oversight is essential...
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